Noise From Turbo Area Under Boost (Stock Turbo)

[pixel8r]

Hi,

Just thought I'd start a new topic on this since the title on the previous one is misleading and i've ruled out the original suspects...

The original post is here: http://www.skylinesaustralia.com/forums/topic/355797-s2-noise-under-bonnet-sounds-like-metal-tapping/

The car is a 2000 Stagea s2 auto - completely stock - including stock boost solenoid and turbo etc.

Ok, so I've narrowed it down to somewhere left of the motor, can only hear it while driving the car - and only above 2500rpm, sometimes above 3000rpm if only light throttle.

Above 3500rpm the sound is more constant, sounds almost like a cricket or cicada if that makes sense.

from 2500 to 3500rpm its more like a tap-tap sound intermittently, cant say whether its metal on metal or some kind of rattle under the bonnet...I'd need it on a dyno to say exactly where its coming from since it only happens near max boost.

It kind of also sounds a bit like fingernails on a blackboard.

What I've ruled out:

* Doesn't seem to be engine related - since it only happens under boost (revving it in neutral sounds very healthy)...and I gave it a full tank of 98 octane so I dont think its pinging or anything...also i'm pretty sure its coming from the left of the engine...

* I dont think it can be internal to the turbo because it only happens under heavier boost which means the turbo is spinning pretty fast. If it was coming into contact with anything at this point it would be more like a loud screech, not a tap-tap or chipping sound. If fins were touching the housing then I'd expect it to screech. it would touch on every revolution which at several thousand rpm would sound like a continual sound, not intermittent.

My current suggestions are:

* is it possible the boost control solenoid is causing this noise? it only seems to happen near max boost...although nowhere near the 4500rpm mark where the solenoid usually activates.

* maybe some vibration causing something to rattle? would loose manifold nuts cause a T-T-T intermittent sound that gets more regular and faster as the revs go up? The turbo is quite loud, but the whistle/whoosh sounds perfectly fine.

* I'm thinking engine and turbo are probably fine, and that something may be loose and causing a rattle...is this likely/possible? would need to be something affected by boost/airflow.

* something to do with the wastegate...could the wastegate be a bit noisy? This would explain it since its near max boost when it happens - right about when I'd expect it to open.

what are your thoughts?

Edited March 3, 2011 by pixel8r

[bubba]

Manifold > turbo gasket

[pixel8r]

Manifold > turbo gasket

Just to follow up - you were quite correct. I got the dealer to replace the gasket and all is well now. Thanks

[bubba]